I don't recall these references ever said "jet black", just that the red read as black (i.e. dark skin) on B&W TVs.

Star Trek 365 does indeed say "jet black."

Gary7 wrote:

Red? Like an American Indian skin tone? That would've backfired, I think. If anything, it would play up the "devil" appearance a bit much, at least on color television. And then on B&W (black and white) sets, he'd have looked more ethnic.

I wish we knew exactly how red Spock's skin was originally supposed to be. If it was as red as Susan Oliver's Orion slave girl makeup was green, I imagine it would have been pretty red. A "red tint" is harder for me to visualize.